Pre-crosslinked gel profile control water shutoff agent and preparation method thereof

Abstract

The invention discloses a pre-crosslinked gel profile control water plugging agent and a preparation method thereof, and relates to the technical field of oil-gas field development. The preparation method of the profile control and water plugging agent comprises the following steps: taking liquid bisphenol A epoxy resin or bisphenol F epoxy resin, adding polyethylene glycol and a curing agent, uniformly stirring to form a mixed solution, adding water-absorbing gel particles under the condition of continuous stirring, stirring, uniformly mixing, curing, and screening to obtain the profile control and water plugging agent. The pre-crosslinked gel profile control and water plugging agent prepared by the invention adopts a core-shell structure, so that water-absorbing expansion particles in the pre-crosslinked gel profile control and water plugging agent do not expand quickly, and the injection cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a pre-crosslinked gel profile control and water plugging agent and a preparation method thereof. Background Art

[0002] Profile control and water plugging agent, also known as diverting agent, is an oilfield auxiliary agent for temporary plugging of cracks. Under its action, high permeability layers can be plugged to facilitate fracturing of low permeability layers. Therefore, it is widely used to plug high permeability layers or reservoirs with strong heterogeneity.

[0003] Gel-type profile control and water plugging agents are currently emerging profile control and water plugging agents, which are usually represented by polyacrylamide gels. Gel-type profile control and water plugging agents are divided into ground-forming gels and underground-forming gels according to their cross-linking timing. Among them, underground-forming gels refer to the injection of polymers and cross-linking agents into the formation, and then the polymers are cross-linked in the formation. Its advantages are low injection pressure and shear resistance. However, underground gelation will cause the gel or frozen gel after gelation to affect more reservoirs, and the subsequent gel breaking viscosity is large, which has a greater impact on the permeability of the reservoir; ground-forming gels refer to the reaction of polymers and cross-linking agents in the factory to make gel particles, which is usually called pre-cross-linked gel. Its advantage is that it has less impact on the reservoir. However, the existing pre-cross-linked gel particles have a fast water absorption and expansion speed. Usually, the expansion rate can reach several times or even more than ten times after absorbing water for 1 hour, resulting in a higher injection cost. At the same time, the volume of the expanded gel particles is larger, and a greater pumping pressure is required to enter the fracture, resulting in an increase in cost. Summary of the invention

[0004] In view of the above technical problems, the purpose of the present invention is to provide a pre-crosslinked gel profile control and water plugging agent and a preparation method thereof in view of the defects of the prior art.

[0005] The present invention adopts the following technical solutions:

[0006] A preparation method of a pre-crosslinked gel profile control and water plugging agent comprises the following steps, measured in parts by weight: taking 30 to 50 parts of liquid bisphenol A epoxy resin or bisphenol F epoxy resin, adding 5 to 15 parts of polyethylene glycol and 5 to 10 parts of a curing agent, stirring evenly to form a mixed liquid, adding water-absorbing gel particles under continuous stirring, stirring and mixing evenly and curing, and then sieving the mixed liquid to obtain a pre-crosslinked gel profile control and water plugging agent; the mass ratio of the mixed liquid to the water-absorbing gel particles is 15 to 25:100.

[0007] For conventional pre-crosslinked gel particles currently used for profile control and water plugging, such as polyacrylamide pre-crosslinked gel particles, they absorb water and swell quickly at room temperature. Usually, they can absorb water and swell by at least 1 times in a few minutes, and the expansion multiple can reach more than dozens of times in 60 minutes. Generally speaking, the injection displacement of profile control and water plugging agents is usually 10 to 20 m 3 / h, for different wells, the injection volume varies from tens to hundreds of cubic meters. In addition, after the profile control and water plugging agent is configured, it usually takes a certain time interval before it is injected into the reservoir (such as performance testing, etc.). Under such circumstances, almost all pre-cross-linked gel particles have expanded before entering the formation. The expansion of these pre-cross-linked gel particles in water usually affects the viscosity of water: when it absorbs water and swells, as the molecular chain unfolds, hydrogen bonds and molecular entanglements are formed between the gel particles, resulting in an increase in viscosity; and the increased viscosity will lead to an increase in pumping pressure; at the same time, the excessive volume of the gel particles after absorbing water and swelling will also lead to an increase in pumping pressure: although the gel after absorbing water can be deformed under pressure, the larger its volume, the greater the force required to cause the gel particles to deform. Therefore, an excessively large volume will lead to an increase in pumping pressure.

[0008] Therefore, in the present invention, epoxy resin is used as the shell layer, which can be well adhered to the surface of the water-absorbing gel particles to form a protective film. Since epoxy resin does not have water-absorbing and swelling properties, it can well protect the profile control and water plugging agent. For epoxy resin, it uses epoxy groups and curing agents for open-ring crosslinking. Although it has certain water resistance, when the profile control and water plugging agent enters the formation, it not only contains a large amount of water around it, but also has a certain temperature in the formation. These conditions will accelerate the degradation of epoxy resin in the formation, so that the water-absorbing gel particles of the profile control and water plugging agent of the present invention can expand rapidly in the formation.

[0009] For epoxy resin, although it can be degraded in high temperature and high pressure reservoirs, its degradation rate is slow. In the present invention, a certain amount of polyethylene glycol is also added to the shell layer. For polyethylene glycol, it has good solubility in water, especially in reservoirs under certain temperature conditions, its dissolution rate is fast. Therefore, it is added to the shell layer. When the profile control and water plugging agent is placed in water, the polyethylene glycol in the shell layer will slowly dissolve, causing holes in the shell layer, which not only reduces the strength of the shell layer, but also allows water to enter the shell layer. When the water-absorbing gel particles absorb water and expand to a certain multiple, the shell layer disintegrates.

[0010] There are many curing agents for epoxy resin, such as conventional amine curing agents, carboxylic anhydride curing agents, etc., which can all be applied to the present invention. Considering the advantages and disadvantages of each curing agent, amine curing agents are preferred, which can promote the curing of epoxy resin at room temperature, and the reaction conditions are relatively mild. At the same time, different curing agents have different curing temperatures and curing times, such as 20 to 80°C for amine curing agents, and the curing time is usually tens of minutes to tens of hours depending on the temperature. Those skilled in the art can determine it according to the actual selected curing agent.

[0011] As for the amount of the mixed liquid and the water-absorbing gel particles, if the amount of the mixed liquid is too large, the thickness of the shell will increase, which will lead to a longer disintegration time of the shell; if the amount of the mixed liquid is too small, the thickness of the shell will be low, which will lead to rapid disintegration of the shell and even make it difficult to form a complete shell on some water-absorbing gel particles. After a large number of experiments by the inventors, it was found that when the mass ratio of the mixed liquid to the water-absorbing gel particles is 15 to 25:100, the thickness of the final shell is just right.

[0012] One embodiment of the present invention is that the molecular weight of the polyethylene glycol is 700 to 1500. For polyethylene glycol, its molecular weight can actually be set wider, such as PEG400 and PEG3000, etc. However, when the molecular weight of polyethylene glycol is too low, the polyethylene glycol in the shell will gradually be discharged from the profile control and water plugging agent under normal temperature conditions, causing the performance of the product of the present invention to decline; when the molecular weight of polyethylene glycol is too large, its solubility in water is poor and it is difficult to play a corresponding role. Therefore, in the present invention, the molecular weight of polyethylene glycol is preferably 700 to 1500.

[0013] In one embodiment of the present invention, the water-absorbing gel particles are one of sodium polyacrylate water-absorbing gel and polyacrylamide water-absorbing gel. These water-absorbing gel particles are conventional water-absorbing gel particles in the art, but when selecting specific water-absorbing gel particles, attention should be paid to their expansion multiple and strength after profile control and plugging to meet subsequent development requirements.

[0014] Furthermore, the water-absorbing gel particles also contain reinforcing nanoparticles, and the mass ratio of the reinforcing nanoparticles to the water-absorbing gel is 1:20 to 30. These nanoparticles can increase the strength of the water-absorbing gel particles.

[0015] Preferably, the water-absorbing gel particles are prepared by the following method: the water-absorbing gel particles are prepared by the following method: taking acrylamide and dissolving it in water, then adding an initiator, a cross-linking agent and reinforcing nanoparticles and reacting, and after the reaction is completed, drying, crushing and granulating; the mass concentration of the acrylamide is 15-25%, the amount of the initiator added is 1-3% of the mass of the acrylamide, and the amount of the cross-linking agent added is 0.1-0.5% of the mass of the acrylic acid. In this process, it can also add conventional functional monomers in the field, such as conventional sodium p-styrene sulfonate, etc.; for the cross-linking agent and initiator, they are all common cross-linking agents and initiators in the field, such as N,N-methylenebisacrylamide and potassium persulfate. However, this is not the focus of the present invention, so the present invention will not elaborate on its specific raw material composition.

[0016] Preferably, the reinforcing nanoparticles are at least one of nano silicon dioxide, nano calcium carbonate, nano iron oxide, and nano zinc oxide, which are common nano materials in the art.

[0017] One embodiment of the present invention is that 5 to 15 parts of acetone are further added to the mixed solution. Acetone is a diluent for epoxy resin and can reduce the viscosity of epoxy resin, thereby making the adhesion between the solidified particles lower and easier to separate.

[0018] One embodiment of the present invention is that the cooling process includes the following steps: taking the mixed material, cooling it to 2 to 10°C below the melting temperature of paraffin and maintaining it for 3 to 20 minutes, then flattening the water-absorbing gel particles and cooling it to room temperature and continuing to cool until the paraffin is completely hardened. The profile control and water plugging agent prepared in this way does not need to be further crushed, and can be directly screened to screen out the profile control and water plugging agent that meets the size requirements.

[0019] Another object of the present invention is to disclose a pre-crosslinked gel profile control and water plugging agent, which is prepared by any of the methods described above.

[0020] The beneficial effects of the present invention are as follows: the pre-crosslinked gel profile control and water plugging agent prepared by the present invention adopts a core-shell structure, so that the water-absorbing and swelling particles inside will not expand rapidly, thereby reducing the injection cost; at the same time, the pre-crosslinked gel profile control and water plugging agent of the present invention has a controllable swelling time and is suitable for most oil reservoirs. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is described in detail below in conjunction with embodiments, but it should not be understood as limiting the scope of implementation of the present invention.

[0022] In the following examples, unless otherwise specified, the methods used are conventional methods in the art.

[0023] In the following examples, unless otherwise specified, the pharmaceutical agents used are conventional commercial products.

[0024] In the following examples, unless otherwise specified, the parts are by mass.

[0025] Example 1

[0026] Preparation of water-absorbing gel particles: Take 220 parts of acrylamide and dissolve it in 800 parts of water. Under the condition of nitrogen deoxygenation, add 3.2 parts of potassium persulfate, 0.5g of N,N-methylenebisacrylamide and 9 parts of nano-silicon dioxide, and react at 65°C for 3h to obtain the water-absorbing gel particles. After the reaction is completed, dry, crush and granulate to obtain the water-absorbing gel particles.

[0027] Preparation of profile control and water plugging agent: Take 40 parts of bisphenol A epoxy resin E51, then add 7 parts of PEG800, 8 parts of diethylenetriamine, and 10 parts of acetone, stir to mix them evenly, add 300 parts of water-absorbing gel particles and mix them evenly under continuous stirring at 30°C, continue stirring for 30 hours, and then sieve it to obtain the agent.

[0028] Example 2

[0029] Preparation of profile control and water plugging agent: Take 32 parts of bisphenol A epoxy resin E51, then add 12 parts of PEG800 and 6 parts of diethylenetriamine, stir to mix evenly, add 300 parts of commercially available pre-cross-linked swelling agent (maximum expansion multiple of 20 times of clean water) under continuous stirring and mix evenly, continue stirring for 30 hours, and then sieve it to obtain the product.

[0030] Example 3

[0031] Preparation of degradable water-absorbing particles: the same as in Example 1.

[0032] Preparation of profile control and water plugging agent: Take 48 parts of bisphenol F epoxy resin EPEF170, then add 7 parts of PEG800 and 9 parts of diethylenetriamine, stir to mix them evenly, add 300 parts of water-absorbing gel particles under continuous stirring and mix evenly, continue stirring for 30 hours, and then sieve it to obtain the agent.

[0033] Example 4

[0034] Compared with Example 1, the difference is that the polyethylene glycol is PEG1200, the curing temperature is 45° C., the curing time is 4 h, and the rest are the same.

[0035] Example 5

[0036] Compared with Example 1, the difference is that the polyethylene glycol is PEG2400, the curing temperature is 55° C., the curing time is 2 h, and the rest are the same.

[0037] Example 6

[0038] Compared with Example 1, the difference is that the polyethylene glycol is PEG600, and the rest are the same.

[0039] Comparative Example 1

[0040] Compared with Example 1, the difference is that polyethylene glycol is not added, and the rest are the same.

[0041] Comparative Example 2

[0042] Compared with Example 1, the difference is that the added amount of bisphenol A epoxy resin is 60 parts, and the rest are the same.

[0043] Comparative Example 3

[0044] Compared with Example 1, the difference is that the added amount of PEG800 is 4 g, and the rest are the same.

[0045] In order to illustrate the effect of the profile control and water plugging agent prepared according to the embodiment of the present invention, a specific example is used to illustrate it.

[0046] Expansion rate test: simulated formation water with a salt content (sodium chloride) of 10,000 mg / L was prepared, and several vials were prepared. An appropriate amount of profile control and water plugging agent and simulated formation water were added to the vials. The water absorption expansion multiples under different temperatures and different time conditions were observed and tested. The test time was 2 hours. The final results are shown in Table 1.

[0047] Table 1 Water absorption expansion test results under different temperature conditions

[0048]

[0049] It can be seen from Table 1 that the profile control and water plugging agent of the embodiment of the present invention basically does not expand under normal temperature conditions. When its expansion multiple reaches a certain critical point (usually about 1.5 times), its expansion multiple increases rapidly, which can meet the existing profile control and water plugging needs. At the same time, it can be seen from Table 1 that its expansion conditions are controllable and can be regulated by temperature and time. Therefore, it can be applied to most of the current reservoir profile control.

[0050] As shown in Comparative Example 1, its expansion speed is slow under low temperature conditions. At present, the amount of drilling fluid in the wellbore varies from tens of cubic meters to tens of cubic meters according to the well depth, and generally speaking, the injection rate of the profile control agent is about 10 to 20 cubic meters per hour. Therefore, generally, after about 3 hours of pumping the profile control agent, the profile control agent segment plug has entered the reservoir. If the profile control agent has not started to expand at this time, the profile control agent may enter the non-target layer, resulting in a decrease in the profile control effect. Therefore, the profile control agent of Comparative Example 1 is difficult to apply to most oil reservoirs; as shown in Comparative Examples 2 and 3, when the amount of material added is changed, its expansion speed is too fast or too slow, which is difficult to meet the actual use requirements.

[0051] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a pre-crosslinked gel profile control and water plugging agent, characterized in that: The method comprises the following steps, in parts by weight: taking 30 to 50 parts of liquid bisphenol A epoxy resin or bisphenol F epoxy resin, adding 5 to 15 parts of polyethylene glycol and 5 to 10 parts of a curing agent, stirring evenly to form a mixed liquid, adding water-absorbing gel particles under continuous stirring, stirring and mixing evenly and curing, and then sieving the mixed liquid to obtain the mixed liquid; the mass ratio of the mixed liquid to the water-absorbing gel particles is 15 to 25:

100.

2. The method according to claim 1, characterized in that The molecular weight of the polyethylene glycol is 700-1500; and the curing agent is an epoxy resin curing agent.

3. The method according to claim 1, characterized in that The water-absorbing gel particles are one of sodium polyacrylate water-absorbing gel and polyacrylamide water-absorbing gel.

4. The method according to claim 3, characterized in that The water-absorbing gel particles also contain reinforcing nanoparticles, and the mass ratio of the reinforcing nanoparticles to the water-absorbing gel is 1:20-30.

5. The method according to claim 4, characterized in that The water-absorbing gel particles are prepared by the following method: taking acrylamide and dissolving it in water, then adding an initiator, a cross-linking agent and reinforcing nanoparticles and reacting them, and after the reaction is completed, drying, crushing and granulating to obtain the water-absorbing gel particles; the mass concentration of the acrylamide is 15-25%, the amount of the initiator added is 1-3% of the mass of the acrylamide, and the amount of the cross-linking agent added is 0.1-0.5% of the mass of acrylic acid.

6. The method according to claim 4 or 5, characterized in that: The reinforcing nanoparticles are at least one of nano silicon dioxide, nano calcium carbonate, nano iron oxide and nano zinc oxide.

7. The method according to claim 1, characterized in that 5 to 15 parts of acetone are also added to the mixed solution.

8. A pre-crosslinked gel profile control and water plugging agent, prepared by the method according to any one of claims 1 to 6.

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